PHYSICOCHEMICAL MEASUREMENTS E N G I N E E R I N G Q U A L I T Y A S S U R A N C E O F MEASUREMENTS P E R T A I N I N G T O C O R R O S I O N OF M E T A L S A. V. Khramov

U D C 389.620.193.08

The protection of metals against corrosion is an important task. It involves many engineering problems the solution of which requires that measurement techniques be developed to facilitate lengthy automated testing of metals for corrosion resistance under natural conditions or under accelerated conditions in the laboratory, as well as automated data processing for predicting the corrosion resistance on the basis of a statistical data evaluation. The problems of automated corrosion measurements have not been dealt with throughly enough and the solutions are not adequate in terms of modern requirements. The-underestimation of their importance results in a tremendous waste of material throughout the national economy. Although neither the physical nor the thermodynamic characteristics of metals must be regarded as tile direct cause of losses due to the breakdown of structures, even rough estimates are still quite indicative. Corrosion measurements can be automated by electrochemical and electrical methods [1-4], electromagnetic methods [5-6], ultrasonic methods [7-9], or radioisotopic methods [10-14]. Electromagnetic, ultrasonic, and sometimes also electrical methods are applicable where the given structure is accessible from one side oniy (ship hulls, boilers, pipes, cabte sheaths, etc.). Ultrasonic penetroscopy seems to be an effective method of such corrosion measurements. Owing to their sufficiently high sensitivity, these methods are useful for measuring slow corrosion rates over long periods of time. Despite the availability of so many diverse methods on the basis of which all modes of metal corrosion could be measured with modem meansof automation, hardly any instruments for corrosion measurements under natural or laboratory conditions are manufactured serially. Oniy specially built prototype and sample models of such instruments are used to a very limited extent in research. One type of instrument alone is beginning to appear on the market now. This author has analyzed the specifications, the catalogs of instruments checked out at the LGN, and the descriptions of existing facilities for the measurement of metal corrosion, and has established the following facts. The engineering characteristics of instruments for corrosion measurements are standardized not on a uniform basis and without regard to existing specifications, thus precluding a technical compatibility between these instruments and others as well as the feasibility of their incorporation in automated apparatus and systems. The nomenclature of engineering characteristics, even where measurements pertaining to the same form of corrosion are concerned, differs from one instrument to another, making it impossible to compare the results of such measurements. An accuracy evaluation of methods used for designing various corrosion test facilities shows no basis of comparison for selecting the best method to suit any specific form of corrosion. In many cases the engineering characteristics of instruments for corrosion measurements have not been standardized at a11. There is a lack of reference standards and other means necessary for checking the instruments used in various corrosion measurements, there is no procedure for testing these instruments, no normative-engineering documentation for regulating and organizing such tests, no normative-engineering documentation to provide the expertise in corrosion measurements and instrument handling. There is no unified terminology applicable to methods and instruments for measuring all the various modes of corrosion. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 78-79, November, 1978.

9 19 76 Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publisher for $15.00.

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instruments manufactured for the defectoscopy of production samples are useful here only in individual cases, for measuring only a few forms of corrosion. Neither the methods of corrosion measurement nor the instruments for this purpose are covered by the overall governmental system of engineering quality assurance. As a consequence, the reliability of information gathered through corrosion measurements in science and in industry cannot be ascertained either analytically or experimentally. Depending on the kind of metal involved as well as on the medium and on the ambient conditions, corrosion may lead to different modes of breakdown and may occur nonuniformly: tarnishing, crevice corrosion, pitting, subsurface corrosion, and intercrystalline corrosion. It is not possible to measure the extent of breakdown with one and the same apparatus in each case. Procedures for qualifying, calibrating, and checking the instruments used in corrosion measurement must ensure: 1) consistent readings regardless of the time and the place of measurement, 2) accuracy of both the methods and the instruments so as to meet the requirements applicable to serial manufacture with the effects of variable ambient conditions properly compensated, and 8) the possibility of reading the corrosion parameters in generally accepted units. Satisfying the requirement that the effect of various factors on the results of corrosion measurements be reduced is very difficult, inasmuch as the physicomechanical properties of test samples, structures, and reference specimens cannot be easily maintained identical. Since instruments for the defectoscopy of production samples are calibrated in linear units [15], while corrosion data are expressed in units of mass, hence the recalculations necessary here reduce the processability and the reliability of these data. In order to improve the reliability of corrosion test data, it is necessary to: develop and organize the manufacture of corrosive breakdown standards or models, develop and organize the serial manufacture of instruments for measuring various forms of corrosion, set up a normative-engineering documentation pertaining to ways and means by which corrosion measuring instruments will be qualified and checked, and organize a periodic inspection of corrosion measuring instruments by the USSR Government Bureau of Standards and by departmental measurementengineering agencies. The setup and excensive use of automated facilities for corrosion measurements, the development of solutions to theoretical and practical problems of engineering assurance in corrosion measurements, and the incorporation of corrosion measuring instruments into the overall governmental system of ensuring consistent measurements will require a huge investment of capitaL Such an investiment will soon pay off in terms of more efficient research as well as through a more reliable control of and protection against corrosion. LITERATURE

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 18.

CITED

V.V. Romanov, Methods of Corrosion Study [in Russian], Izd. Metallurgiya, Moscow (1965). P . A . Akol'zin and E. N. Ivanov, in: New Methods of Studying the Corrosion of Metals [in Russian] (editor: I. L. Rozenferd), Izd. Nauka, Moscow (1978). A . V . Khramov, Author's disclos. No. 428016, Byuli. Izobret., No. 13 (1974). A.V. Khramov, deposition inNIIT~Khim, No. 177/74, February, 1974. G . A . Grinberg, Selected Problems in the Mathematical Theory of Electrical and Magnetic Phenomena [in Russian], Izd. Akad. Nauk SSSIL Moscow-Leningrad (1948). C.N. Owston, Brit. I. Nondestmct. Test., 13__, No. 6 (1971). M . I . Vit'ko et al., in: Nondestructive Methods of Materials and Parts Inspection [in Russian], Izd. ONTIpribor, Moscow (1964). D . V . Vladimirova et aL, in: Nondestructive Methods of Materials and Parts inspection [in Russian], Izd. ONTIpdbor, Moscow (1964). N . I . Blazhnikov Ultrasonic Methods [in Russian], Izd. Energiya, Moscow (1968). E. Schasche and R. L. Little, US Patent No. 3101413,Class 280-106 (1959). O. Aladjem and I. Yahalom, Israel Atomic Energy Commission Report No. 1190 (1969). S. Popov, in: Nondestructive Methods of Materials and Parts Inspection [in Russian], Izd. ONTIpribor, Moscow (1964). A.V. Khramov and N. G. Martynova, Deposition in VINITI, No. 8080/72 (1972). N . G . Martynova and A. V. Khramov, in: Natural and Accelerated Corrosion Tests [in Russian], Izd. F. E. Dzerzhinskii DNTP, Moscow (19"/2). Yu. A. Koltashev et a1., Thickness Control of Protective and Special Coatings[inRussian], Izd. VNIIKI, Moscow (1971). 1687